Integrated circuit designers have always sought the ideal semiconductor memory—a device that is randomly accessible, can be written and read very quickly, is non-volatile, but indefinitely alterable, and consumes little power. Resistive memories, including programmable contact random access memory (PCRAM) technology has been increasingly viewed as offering all these advantages.
Digital memories are widely used in computers, computer system components and computer processing systems. Resistive memories store digital information in the form of bits or binary digits as “0”s or “1”s based on the resistance of a memory element or cell. Resistive memory devices are configured in arrays where a resistive element or cell is at the intersection of a row line (word line) and a column line (digit line or bit line). In order to read or sense the state of a memory cell, it is necessary to first select the desired memory cell by selecting the column line and row line, which intersect at the desired memory element. Once the desired memory element is isolated, the selected memory cell is then read by applying a read voltage to the cell to detect the resistance of the memory cell and thereby, determine the logic state of the memory cell.
For binary logic state sensing, the absolute magnitude of memory cell resistance need not be known, only whether the resistance of a memory cell is above or below a threshold value that is between logic one and logic zero resistance values. Nonetheless, sensing the logic state of a PCRAM memory element is difficult because the technology of the PCRAM device imposes multiple constraints.